Quantitative ultrasound elastography measures tissue viscoelasticity by applying ultrasound radiation force to a tissue region, measuring the propagation properties of induced shear waves, such as displacements and propagation velocities (group velocity or phase velocity), and calculating viscoelasticity of the tissue. These technologies include ultrasound vibrometry (U.S. Pat. Nos. 7,753,847, 7,785,259, 8,659,975, 8,602,994), ARFI (US 20050215899), Supersonic shear Imaging (SSI) and Shear wave Spectroscopy (SWS) (U.S. Pat. No. 8,150,128), and other similar techniques such as Shear Wave Elasticity Imaging (SWEI), Spatially Modulated Ultrasound Radiation Force (SMURF), Crawling Wave Sonography (CWS).
Above said methods assume that tissue response to excitation pulses are linear, so that the measurements of tissue property such as group velocity and phase velocity of shear wave are independent to excitation pulse widths and shapes, as the said velocities are used to calculate the tissue viscoelasticity for charactering tissue shear property.
Above said methods do not measure tissue nonlinearity, nor consider the impact of the nonlinearity to the accuracy of the estimates of the tissue viscoelasticity.
Above said methods require the detection of shear wave at multiple locations to estimate shear wave velocities in order to calculate the viscoelasticity of tissue.